Device for annealing glass panes

ABSTRACT

A device for annealing glass panes includes rollers for transporting the glass panes and two sets of slit-shaped nozzles, which run parallel to the axes of the rollers and from which cooling air can be directed onto both sides of the glass panes. In the device, cooling air acts as effectively as possible on the two surfaces of the glass pane, and anisotropies and stresses within the glass are reduced. This can be achieved by each nozzle being formed as a continuous flow channel, which extends over the width of the glass panes and on both parallel running sides of which partitions are arranged, for the forming of a flow pocket assigned to this flow channel. The cooling air that comes back from the glass panes is returned between this flow channel and the associated partitions.

The invention concerns a device for annealing glass panes according tothe preamble of claim 1.

It is known from the prior art, for example, DE 10 2008 045 416 A1, thatglass panes can be thermally prestressed. So-called tempered safetyglass is produced by the process of thermal prestressing. During thermalprestressing, a tensile stress is produced by heat treatment (annealing)on the interior of the glass pane and a compressive stress on thesurfaces and on the edges. Compressive stresses develop in the glassbecause of this, which leads to increased tensile bending strength ofthe glass panes thus produced. The glass is also more resistant totemperature differences and shatters into small fragments when destroyedthereby resulting in a lower risk of injury.

Annealing generally occurs by first heating the entire glass pane to thesoftening point of the glass and then subjecting it to rapid cooling. Inthis way, however, more or less strong undesired anisotropies in theform of color defects develop as a result of birefringence duringillumination with at least partially polarized light.

EP 2 853 517 B1 also deals with this problem and proposes an annealingprocedure in which the glass pane is moved back and forth in a furnaceand then guided to two cooling areas, in which, in the first coolingarea, cooling air is directed onto the surface of the glass panesthrough slit nozzles and, in the second cooling area cooling air isdirected onto the surface of the glass panes through hole-like nozzles,in which case the glass pane is moved back and forth in both coolingareas on rollers. Both surfaces of the glass pane can be cooled withcooling air in both cooling areas. The rollers on which the glass panesare guided are fully wrapped with cords.

However, interfering anisotropies in the glass panes are still generatedin this procedure. Guiding of the cooling air is also irregular,turbulent and not very effective.

The object of DE 693 12 169 T2 is a method and device for producing bentglass panes, which are heated to a bending temperature by passing theseglass panes past a shaping bed with an essentially circular and conicalguide profile, the shaping bed being formed from an arrangement ofrollers that drive the glass pane, and the bed being formed from a hotair cushion. The rollers here extend to both sides of the glass panebeing transported and bent and are in contact with the glass pane onboth sides. Flow channels are arranged between the rollers. DocumentsU.S. Pat. No. 3,881,907, EP 1 957 419 B1 and U.S. Pat. No. 4,820,327also deal with methods and devices for annealing glass panes and showslit-like nozzles as well as partitioning of an annealing station intoseveral parts.

A drawback of the described device and method presented is the highdemand on the guide rollers, which are to be arranged on both sides ofthe glass pane and adjusted so that the upper guide rollers also exertan identical pressure on the glass pane as the lower guide rollers onwhich the glass pane rests by its own weight. The device is thereforecomplex and expensive to produce and operate.

The task is therefore to develop a device for annealing of glass panesthat is suitable to produce and operate and in which the cooling airacts as effectively as possible on both surfaces of the glass pane andanisotropies are also reduced within the glass.

This task is solved with the characterizing features of claim 1.Advantageous embodiments can be deduced from the dependent claims.

A practical example of the invention is further explained below withreference to the accompanying drawing. This shows a perspective sideview of a glass pane in an annealing device according to the inventionin which the cooling air flow is shown by arrows.

The FIGURE shows a glass pane 1, which is subjected to annealing in thedevice shown. The underside of the glass pane 1 lies on rollers 2, whichare mounted so as to rotate about axes 3. The glass pane 1 can betransported on these rollers 3 or also moved back and forth, by drivingthe rollers 3 accordingly, which is not shown in detail. The rollers 3are provided with a coating which can be a strip consisting of aramid orKevlar or another appropriate material. The choice of coating isdetermined by the high temperature of the heated glass coming from thefurnace, which is between 600 and 700° C.

A flow channel 4, which extends over the width of the glass pane and isdesigned continuous, is situated between two adjacent rollers 2. Asshown in the FIGURE, the walls of the flow channel 4 extend betweenadjacent rollers 2 so that the cooling air 6 emerges from the flowchannels 4 in the direction toward the underside of the glass pane 1 inthe region of the joining plane of the axes 3 of rollers 2 or even afterthem, i.e., closer to the underside of the glass pane 1. As shown in theFIGURE, the flow channels 4 are initially wide and then increasinglynarrow in the direction toward the glass pane 1 so that a tapering flowchannel is formed that extends over the entire width of the device,i.e., the length of the rollers 2 and the width of the glass pane 1. Thetapering structure of these flow channels 4 corresponds roughly to aninverted “V”.

Since the rollers 3 are situated between adjacent flow channels 4,which, since they carry the glass pane 1, extend right up to it, theindividual flow channels are shown in the FIGURE by the arrowsindicating the air flow. Each flow parcel has a flow channel 4 thatsupplies the cooling air 6. This is then reflected on the underside of aglass pane 1 and directed outward in the direction toward the rollers 3and then deflected downward so that it flows laterally from the flowchannel 4.

The top of the glass pane 1 facing away from rollers 2 is also exposedto cooling air 7, which flows from identically or similarly designedflow channels 5 that are arranged above the glass pane 1 and also haveroughly the cross-sectional shape of a “V” so that they form acontinuous flow channel via which cooling air 7 is blown onto the uppersurface of the glass pane 1. The upper flow channels 5 also extend overthe entire width of the device, i.e., the length of the rollers 2 andthe width of the glass pane 1. The upper flow nozzles 5 are arranged sothat they are roughly flush with the lower opposite flow channels.

There are no rollers 2 above the glass pane 1 for forming a naturalpartition between the flow channels 5. For this reason, partitionsformed by wall elements 9 are formed between the upper flow channels 5,whose distance to the glass panes 1 is as small as possible duringoperation of the device and is a maximum of 10 mm. The wall elements 9run parallel to the flow channels 5.

Owing to the arrangement, flow parcels are formed both beneath the glasspane 1 and above the glass pane 1. During operation of the device,cooling air 6 is guided in the direction of the underside of the glasspane 1 by the flow channels 4 arranged beneath the glass pane 1. Thiscooling air 6 is marked by flow arrows. The cooling air 6 strikes theunderside of the glass pane 1 approximately orthogonally, is deflectedtherefrom to both sides and then strikes the top of coated rollers 2.Owing to continuous coating of the rollers 2, a fully closed flow cellis created here and the cooling air 6 is then diverted downward andguided out into the open on both outer sides of the flow channel 4.

Flow occurs similarly on the top of glass pane 1. The cooling air 7 isblown out from the flow channels 5 downward in the direction of the topof glass pane 1, diverted from there leftward and rightward until itreaches the wall elements 9 extending just above the top of glass pane1. The largest portion of the cooling air 7 is then diverted upward onthese wall elements 9 and reaches the outside via the outer sides of theflow channel 5.

By means of the arrangement according to the invention, defined flowparcels are produced both beneath the glass pane 1 and above the glasspane 1, which are formed beneath the glass pane 1 by two adjacentrollers 2 and above the glass pane 1 by two adjacent wall elements 9.Due to the continuous, very wide flow channels 4 and 5, it is alsopossible to guide a considerable amount of air at low speed, i.e., ahigh volume of air at low pressure, onto both sides of the glass pane 1,which in turn enables a laminar flow at high cooling performance. Byeliminating any turbulence and by means of this laminar flow, not onlyis a more uniform cooling of the glass pane 1 and therefore a loweroptical anisotropy guaranteed, but also a higher efficiency of thecooling performance, which requires up to 50% less energy than knownsystems.

A significant improvement in tensile bending strength of the treatedglass panes is also obtained by applying the device according to theinvention. Due to the more uniformly applied prestressing in the glass,the limit stresses leading to breakage are not reached as early as inthe method according to the prior art.

1-3 (canceled).
 4. A device for annealing glass panes, the devicecomprising rollers on which the glass panes can be transportedhorizontally, and first and second sets of cooling air feeds runningparallel to axes of the rollers, from which cooling air can be guidedonto both sides of the glass pane, each cooling air feed extending overthe width of the glass panes, and partitions being arranged on bothparallel sides of each cooling air feed, in which return of the coolingair reflected back from the glass panes occurs between the partitions,the first set of cooling air feeds being arranged between the rollersand the rollers forming partitions, and the second set of cooling airfeeds being arranged on the top of the glass panes opposite the rollers,and the partitions being formed by wall elements, wherein a distancebetween the wall elements and the glass panes is no more than 10 mm, thecooling air feeds are designed as slit-like nozzles, each nozzle beingdesigned as a continuous tapering flow channel extending over the widthof the glass panes, which forms a flow parcel with the partitions, andthe return of the cooling air reflected back from the glass panes occursbetween this flow channel and the corresponding partitions, whereby theflow rate through the flow channels is limited that laminar flows formin the flow parcels.
 5. The device according to claim 4, wherein therollers are fully wrapped or coated.